Control measures what degree of choice each space represent for its immediate neighbours as a space to move to. Each space has a certain number k of immediate neighbours. Each space therefore gives to each of its immediate neighbours 1/k, and these are then summed for each receiving space to give the control values of that space. Spaces which have a control value greater than 1 will have strong control, those below 1 will be weak control spaces. A typical example is a hospital corridor, which is connected to many one-connected offices.
Hillier, B. & Hanson, J. (1984), The Social Logic of Space, Cambridge University Press: Cambridge. pp.109